A surge protector or arrester is commonly connected across a comparatively expensive piece of electrical equipment to shunt over-current surges. Such over-current surges occur, for example, when lightning strikes. When this happens, the surge arrester shunts the surge to ground, thereby protecting the piece of electrical equipment and the circuit from damage or destruction.
Present day surge arresters commonly include an elongated, hollow cylindrical housing made of porcelain or the like, and a plurality of non-linear resistive blocks within the housing. Some of these structures also include spark gaps, the blocks and gaps being electrically interconnected to handle voltage and current surge conditions arising on a power line. The blocks commonly contain silicone carbide (SIC) or metal oxide varistors (MOV), and are usually in the shape of relatively short cylinders stacked within the arrester housing. The number of blocks employed is a function of the material (SIC or MOV) and the voltage and current ratings of the assembly.
For a surge arrester to function properly, intimate contact must be maintained between the MOV or SIC blocks. This necessitates placing an axial load on the blocks within the housing. Prior art arresters utilize bulky contact springs within the housing to provide this axial load. Typically, these springs can provide only relatively small loads, for example, about sixty pounds. As a result, prior art surge arresters experience one or more problems such as poor heat transfer between the MOV or SIC blocks and arrester terminals; non-uniform current distribution; and high contact resistances at joints. Furthermore, units having low contact force sputter and the ionized metal which is produced can cause axial flashover at high currents.
An additional problem with surge arresters of the prior art is that they, on rare occasions, fail in a dangerous fashion. When these arresters fail and experience high fault currents, the bursting unit may throw parts and cause property damage.
Examples of prior art surge arresters are disclosed in the following U.S. Pat. Nos. 2,587,587 to Bellezza et al.; 3,412,273 to Kennon et al.; 3,524,107 to Reitz; 3,566,183 to Olsen; 3,706,009 to Reitz; 3,973,172 to Yost; 3,987,343 to Cunningham et al.; 4,092,694 to Stetson; 4,100,588 to Kresge; 4,218,721 to Stetson; 4,404,614 to Koch et al.; 4,467,387 to Bergh et al.; and U.S. Defensive Publicaton No. T102,103, as well as U.K. Pat. No. 730,710.